This invention relates to a half thrust bearing.
A thrust bearing for bearing a thrust load, for example, of a crankshaft of an engine, comprises two half thrust bearings, and one of the two half thrust bearings is mounted on a cylinder block while the other half thrust bearing is mounted on a bearing cap.
In this half thrust bearing, a step G (see FIG. 10) is sometimes formed between bearing surfaces of the two half thrust bearings 1 and 2 because of the processing accuracy of the half thrust bearings, the assembling accuracy for the cylinder block and the bearing cap, and the thermal expansion difference between the cylinder block and the bearing cap. In this case, a thrust collar of the crankshaft is abutted hard against confronting ends (that is, localized portions) of the half thrust bearings 1 and 2, and as a result a bearing alloy is subjected to premature fatigue, or is separated. In order to prevent this, a thrust relief 4 is formed at each of circumferentially-spaced opposite (both) end portions of the bearing surface of each of the conventional half thrust bearings 1 and 2, the thrust relief 4 being slanting toward the confronting end of the half thrust bearing progressively away from the bearing surface. Alternatively, the confronting ends of the bearing surface are chamfered. With these methods, the local contact has been alleviated.
In order to prevent seizure and premature fatigue due to the local abutment, it is preferred that the thrust reliefs 4 and the chamfered portions are increased in size. However, this reduces the pressure-receiving area (bearing surface area), so that the thrust load carrying capacity is lowered. In order to compensate for the reduction of the pressure-receiving area, it is necessary to decrease the inner diameter of the half thrust bearing or to increase the outer diameter thereof.
However, if the inner diameter of the half thrust bearing is decreased, the diameter of the crankshaft must be decreased, and the radius of a fillet between a journal portion and a thrust collar portion must be decreased, and this may affect the strength of the crankshaft. If the outer diameter of the half thrust bearing is increased, the thrust collar of the crankshaft must be increased, too, and therefore the overall weight of the engine increases, and besides the friction between each half thrust bearing and the thrust collar increases, so that the efficiency of the engine is lowered.
Thus, to increase the size of the thrust reliefs 4 and the chamfered portions, and to compensate for the reduction of the pressure-receiving area, resulting therefrom, invite the various problems, and therefore are not practical.
Although one half thrust bearing 2 is retained on the cylinder block 5 or the bearing cap 6 against rotation, the other half thrust bearing 1 is not retained against rotation, and therefore moves in the circumferential direction in accordance with the rotation of the crankshaft. At this time, if a step is formed between the cylinder block 5 and the bearing cap 6 as shown in FIG. 10, the confronting ends of the half bearing 1 strike against this step portion, and are plastically deformed, and an end play of the half thrust bearing 1 is increased because of the presence of a recess 7 resulting from this plastic deformation, which leads to a possibility that abnormal noises are produced or to a possibility that the deformation further proceeds, and develops into a crack.